Mineral Information and Data:

Allophane
Al2O3(SiO2)1.3-2.0 • 2.5-3.0H2O [CNMNC approved formula]

Named from the Greek allos - "other" and phanos - "to appear" in allusion to its change when blowpiped.

IMA status : Valid species (Pre-IMA 1816) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
71.01.04.01  
  (71) Phyllosilicate Sheets of Six-Membered Rings
  (71.01) with 1:1 layers
  (71.01.04) Allophane group
  
Nickel-Strunz
(10th edition) :
09.ED.20
  (09) Silicates
  (09.E) Phyllosilicates
  (09.ED) Phyllosilicates with kaolinite layers composed of tetrahedral and octahedral nets
  
Crystal system: Amorphous — no crystals
Point group (H-M): none — no crystals
Crystal Habit: Massive; as crusts resembling hyalite Opal; also stalactitic or powdery aggregates.
  
Color: Colorless, white, green, bluish, yellow, brown
Diaphaneity: Transparent to translucent
Luster: Vitreous, resinous or waxy
Hardness (Mohs): 3
Measured Density: 2.72 -2.788 g/cm3
Tenacity: Brittle
Fracture: Conchoidal to earthy
Streak: Colorless, white
  
Geologic Setting: A weathering product of volcanic ash. In hydrothermally altered igneous rocks, from the breakdown of feldspars, and in hydrothermal veins, typically related to copper deposits. In sedimentary rocks, including chalk and coal beds.
Mineral Association: Quartz, cristobalite, imogolite, gibbsite, vermiculite, chrysocolla, "limonite"
  

 

Allophane
Blue cuprian allophane
Origin: Reiche Zeche Mine, Himmelfahrt Mine, Freiberg, Freiberg District, Erzgebirge, Saxony, Germany
Picture size: 5 mm
Owner: Thomas Witzke

 

Allophane
White massive allophane in a brecciated beige-ocre argillic matrix,
collected in 1938
Origin: Chessy, Rhône, France
Sample size: 3 x 3.5 x 5 cm
Photo: Diederik Visser

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